Waste heat is often created as a byproduct of industrial processes where flowing streams of high-temperature liquids, gases, or fluids must be exhausted into the environment or removed in some way in an effort to maintain the operating temperatures of the industrial process equipment. Some industrial processes utilize heat exchanger devices to capture and recycle waste heat back into the process via other process streams. However, the capturing and recycling of waste heat is generally infeasible by industrial processes that utilize high temperatures or have insufficient mass flow or other unfavorable conditions.
Waste heat can be converted into useful energy by a variety of turbine generator or heat engine systems that employ thermodynamic methods, such as Rankine cycles. Rankine cycles and similar thermodynamic methods are typically steam-based processes that recover and utilize waste heat to generate steam for driving a turbine, turbo, or other expander connected to an electric generator or pump. An organic Rankine cycle utilizes a lower boiling-point working, fluid, instead of water, during a traditional Rankine cycle. Exemplary lower boiling-point working fluids include hydrocarbons, such as light hydrocarbons (e.g., propane or butane) and halogenated hydrocarbons, such as hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) (e.g., R245fa). More recently, in view of issues such as thermal instability, toxicity, flammability, and production cost of the lower boiling-point working fluids, some thermodynamic cycles have been modified to circulate non-hydrocarbon working fluids, such as ammonia.
The heat engine systems often utilize a turbopump to circulate the working fluid that captures the waste heat. The turbopump, as well as other rotating equipment used in the systems, typically generates thrust and other loads that arise in the system during operation and need to be minimized to reduce damage to system components. One way to handle the thrust and other load imbalances in the system is to utilize bearings, such as hydrostatic bearings, to absorb the excessive loads. In high density machinery operating with supercritical fluids, such as supercritical carbon dioxide, it may be desirable to operate the hydrostatic bearings with liquid or supercritical fluid. However, the supercritical fluid is heated as it is circulated through the bearings of the turbopump and, when drained, may experience a large pressure drop. This pressure drop may lead to erosion and/or cavitation of various components of the turbopump, thereby increasing component wear.
Therefore, there is a need for systems and methods that enable use of a supercritical fluid in the bearings of a heat engine system while reducing or eliminating the likelihood of erosion and/or cavitation.